Transmissive Metasurface Lens Integration

ABSTRACT

Metasurface elements, integrated systems incorporating such metasurface elements with light sources and/or detectors, and methods of the manufacture and operation of such optical arrangements and integrated systems are provided. Systems and methods for integrating transmissive metasurfaces with other semiconductor devices or additional metasurface elements, and more particularly to the integration of such metasurfaces with substrates, illumination sources and sensors are also provided. The metasurface elements provided may be used to shape output light from an illumination source or collect light reflected from a scene to form two unique patterns using the polarization of light. In such embodiments, shaped-emission and collection may be combined into a single co-designed probing and sensing optical system.

CROSS-REFERENCE TO RELATED APPLICATIONS

The current application is a continuation of U.S. patent applicationSer. No. 15/931,184, filed May 13, 2020, which is a continuation of U.S.patent application Ser. No. 16/120,174, filed Aug. 31, 2018, whichapplication claims priority to U.S. Provisional Patent Application No.62/552,455, filed Aug. 31, 2017, the disclosures of which areincorporated herein by reference.

FIELD OF THE INVENTION

The current disclosure is directed optical arrangements of metasurfaceelements, integrated systems incorporating light sources and/ordetectors with such metasurace elements, and methods of the manufactureof such optical arrangements andintegrated systems.

BACKGROUND OF THE INVENTION

Metasurface elements are diffractive optics in which individualwaveguide elements have subwavelength spacing and have a planar profile.Metasurface elements have recently been developed for application in theUV-IR bands (300-10,000 nm). Compared to traditional refractive optics,metasurface elements abruptly introduce phase shifts onto light field.This enables metasurface elements to have thicknesses on the order ofthe wavelength of light at which they are designed to operate, whereastraditional refractive surfaces have thicknesses that are 10-100 times(or more) larger than the wavelength of light at which they are designedto operate. Additionally, metasurface elements have no variation inthickness in the constituent elements and thus are able to shape lightwithout any curvature, as is required for refractive optics. Compared totraditional diffractive optical elements (DOEs), for example binarydiffractive optics, metasurface elements have the ability to impart arange of phase shifts on an incident light field, at a minimum themetasurface elements can have phase shifts between 0-2π with at least 5distinct values from that range, whereas binary DOEs are only able toimpart two distinct values of phase shift and are often limited to phaseshifts of either 0 or 1π. Compared to multi-level DOE's, metasurfaceelements do not require height variation of its constituent elementsalong the optical axis, only the in-plane geometries of the metasurfaceelement features vary.

BRIEF SUMMARY OF THE INVENTION

The application is directed to optical arrangements of metasurfaceelements, integrated systems incorporating light sources and/ordetectors with such metasurace elements, and methods of the manufactureof such optical arrangements andintegrated systems.

Many embodiments are directed to methods for fabricating one or moremetasurface elements or systems including:

-   -   depositing a hard mask material layer on at least one surface of        a substrate, wherein the substrate is transparent to light over        a specified operational bandwidth;    -   depositing a pattern material layer on the hard mask material        layer;    -   patterning the pattern material to form an array pattern atop        the hard mask layer, the array pattern comprising one of either        a positive or negative reproduction of a metasurface feature        array, the metasurface feature array comprising a plurality of        metasurface features having feature sizes smaller than the        wavelength of light within the specified operational bandwidth        and configured to impose a phase shift on impinging light within        the plane of plurality of metasurface features;    -   etching the hard mask layer using an anisotropic etch process to        form a plurality of voids and raised features corresponding to        the array pattern in the hard mask; and    -   removing any residual pattern material from atop the hard mask        layer.

In many other embodiments, the substrate is formed of a materialselected from the group consisting of: fused silica, sapphire,borosilicate glass and rare-earth oxide glasses.

In still many other embodiments, the hard mask material layer is formedof a material selected from the group consisting of: silicon, siliconnitride of various stoichiometries, silicon dioxide, titanium dioxide,alumina, and is disposed using a deposition process selected from thegroup consisting of: sputtering, chemical vapor deposition, and atomiclayer deposition.

In yet many other embodiments, the pattern material layer is formed fromone of either a photoresist patterned using a lithographic process, or apolymer patterned using a nanoimprint process.

In still yet many other embodiments, the array pattern is etched using areactive ion etching process selected from the group consisting of: SF₆,C₁₂, BCl₃, C₄F₈ or any static or multiplexed mixture thereof.

In still yet many other embodiments, the residual pattern material isremoves using a process selected form the group consisting of: chemicalsolvent, chemical etchant, and plasma etchant.

In still yet many other embodiments, the patterned hard mask material isa dielectric and forms the metasurface features of the metasurfaceelement.

In still yet many other embodiments, the methods further includes:

-   -   depositing a dielectric metasurface material layer on the        patterned hard mask material layer such that the metasurface        material layer fills the voids in the hard mask material layer        and extends above the raised features of the hard mask material        layer forming an over-layer of metasurface material atop the        hard mask layer; and    -   planarizing the over-layer such that the metasurface material        layer and the hard mask layer terminate at a uniform height        above the substrate.

In still yet many other embodiments, the metasurface material layer isformed from a material selected from silicon, silicon nitride of variousstoichiometries, silicon dioxide, titanium dioxide, alumina, and isdeposited using a conformal process selected from the group of: chemicalvapor deposition, and atomic layer deposition.

In still yet many other embodiments, the planarization uses a processselected from an etch process selected from the group consisting of wetetch and a plasma etch, or a chemical-mechanical planarizationtechnique.

In still yet many other embodiments, the metasurface material disposedin the voids forms the metasurface features of the metasurface element,and wherein the hard mask material is configured as an embeddingmaterial having a lower index of refraction at the specified operationalbandwidth than the metasurface material.

In still yet many other embodiments, the hard mask material hasnegligible absorption over the specified operational bandwidth and hasan index of refraction at the specified operational bandwidth betweenabout 1 and about 2.4

In still yet many other embodiments, the method further includesremoving the hard mask material layer using a selective etch such thatthe metasurface material layer disposed in the voids of the patternedhard mask remains on the surface of the substrate after removal of thehard mask material layer to form a plurality of isolated metasurfacefeatures separated by a plurality of air gaps.

In still yet many other embodiments, the method further includesdepositing an embedding material layer on the isolated metasurfacefeatures such that the air gaps between the features are filled and suchthat the embedding material layer extends above the surface of themetasurface material layer, wherein the embedding material layer has alower index of refraction at the specified operational bandwidth thanthe metasurface material.

In still yet many other embodiments, the embedding material is a polymerselected form the group consisting of poly(methyl methacrylate), SUB,and benzocyclobutene.

In still yet many other embodiments, the embedding material is a solidfilm selected from the group consisting of silicon dioxide, aluminumoxide, titanium dioxide, silicon nitride, hafnium oxide, zinc oxide, andspin-on-glass.

In still yet many other embodiments, the method further includesplanarizing the embedding material layer such that the metasurfacematerial layer and the embedding material layer terminate at a uniformheight above the substrate.

In still yet many other embodiments, the method further includesdepositing an anti-reflective coating atop one or both the embeddingmaterial layer and the side of the substrate disposed opposite themetasurface element.

In still yet many other embodiments, the antireflective coating iscomposed of alternating layers of any combination of materials selectedfrom the group consisting of silicon dioxide, titanium dioxide, aluminumoxide, silicon nitride, aluminum nitride, and amorphous silicon, whereineach of the alternating layers has a thickness less than the wavelengthof light within the operational bandwidth.

In still yet many other embodiments, the substrate is one of eitherdisposed atop an illuminator or sensor, or is itself an illuminator orsensor.

In still yet many other embodiments, the substrate has a substratethickness unsuitable for use with a target optical system at and furthercomprising at least one of the following:

-   -   removing at least a portion of the backside of the substrate        through one or both grinding or chemical etching; and    -   aligning and fusing an additional substrate to the substrate of        the metasurface element.

In still yet many other embodiments, the additional substrate itself hasa metasurface element disposed on one surface thereof, and wherein thesubstrate and additional substrate are fused along surface opposite thesurfaces on which the relative metasurface elements are disposed.

In still yet many other embodiments, the method of fusing uses a bondingprocess having a thermal budget below 600° C.

In still yet many other embodiments, the bonding process is a waferbonding process using an adhesive selected from the group of an opticalepoxy, benzocyclobutene, a UV cured polymer, SU8, and a plasma activatesilicon dioxide film.

In still yet many other embodiments, the method further includesremoving at least a portion of the backside of one or both of thesubstrates prior to fusing.

In still yet many other embodiments, the method further includes formingat least a first metasurface element on a first side of a firstsubstrate, and forming at least a second metasurface element on a firstside of a second substrate, and fusing the first and second substratestogether along sides opposite the first sides of said substrates using abonding process having a thermal budget below 600° C.

In still yet many other embodiments, the plurality of metasurfacefeatures are inhomogeneous.

In still yet many other embodiments, the plurality of metasurfacefeatures diverge from an ideal shape by a pre-determinable amount basedon the dimensions of the metasurface features.

In still yet many other embodiments, the metasurface element is embeddedand planarized and comprises two layers of metasurface features offsetfrom each other by a distance smaller than or on the same order as thewavelength of light within the specified operational bandwidth such thatthe two layers of metasurface features operate in conjunction to imposea phase shift on impinging light.

In still yet many other embodiments, the plurality of metasurfacefeatures are inhomogeneous and diverge from an ideal shape by apre-determinable amount based on the dimensions of the metasurfacefeatures, and wherein the ideal shape is a square, and where the idealsquare has a side dimension of less than 200 nm the metasurface featuresare formed as circles, and where the ideal square has a side dimensionof less than 300 nm the metasurface features are formed as squareshaving rounded edges.

In still yet many other embodiments, the method further includes:

-   -   forming a plurality of identical or unique first metasurface        elements;    -   providing a plurality of identical or unique illumination        sources disposed in a planar array and integrating at least one        of the plurality of first metasurface elements with each of the        plurality of illumination sources in the array such that light        from each of said plurality of illumination sources passes        through at least one of the first metasurface elements and an        angular deflection is imposed thereby;    -   disposing a first spacer layer between the planar array of        illumination sources and the first metasurface elements, the        first spacer layer being configured to create divergence in        light emitted from each of the illumination sources of the        planar array prior to impinging on the respective first        metasurface element;    -   disposing a second metasurface element at a distance from the        plurality of first metasurface elements, the second metasurface        element configured to imprint a far-field illumination pattern        onto a light field formed by the emission of all of the        plurality illumination sources; and    -   disposing a second spacer layer between the first and second        metasurface elements such that an offset distance is formed        therebetween.

Various embodiments are directed to methods of forming amulti-metasurface element comprising forming at least a firstmetasurface element on a first side of a first substrate, and forming atleast a second metasurface element on a first side of a secondsubstrate, and fusing the first and second substrates together alongsides opposite the first sides of said substrates using a bondingprocess having a thermal budget below 600° C.

In various other embodiments, the bonding process is a wafer bondingprocess using an adhesive selected from the group of an optical epoxy,benzocyclobutene, a UV cured polymer, SU8, and a plasma activate silicondioxide film.

In still various other embodiments, the method further includes removingat least a portion of the backside of one or both of the substratesprior to fusing.

In yet various other embodiments the method further includes:

-   -   embedding and planarizing at least one of the first and second        metasurface elements;    -   forming at least a third metasurface element on a first side of        a third substrate; and    -   fusing the side of the third substrate opposite the first side        to the planarized first or second metasurface using a bonding        process having a thermal budget below 600° C.

In still yet various other embodiments, the planarization furthercomprises embedding at least one of the first and second metasurfaceelements in one of either a polymer or a solid-state bonding agent.

In still yet various other embodiments, the method further includesiterating the steps of forming, embedding, and fusing to form a layeredstack of four or more metasurface elements.

In still yet various other embodiments, at least one of layers of at oneend of the layered stack is one of either an illuminator or a sensor.

In still yet various other embodiments, the method further includes:

-   -   inserting a spacer substrate between the sides of the first and        second substrates opposite the metasurface elements, the spacer        substrate having at least one aperture disposed therethrough;        and    -   fusing the spacer substrate to the first and second substrates        using a bonding process having a thermal budget below 600° C.,        such that the at least one aperture forms an air gap between the        first and second substrates.

In still yet various other embodiments, the spacer substrate is formedof a low-index of refraction material selected from the group of:polymer, SiO₂, and glass.

In still yet various other embodiments, the spacer material is coated inblack chrome.

In still yet various other embodiments, the method further includesiterating the steps of forming, inserting, and fusing to form a layeredstack of three or more metasurface elements.

In still yet various other embodiments, at least one of layers at oneend of the layered stack is one of either an illuminator or a sensor.

In still yet various other embodiments, the plurality of metasurfacefeatures are inhomogeneous.

In still yet various other embodiments, the plurality of metasurfacefeatures diverge from an ideal shape by a pre-determinable amount basedon the dimensions of the metasurface features.

Further embodiments are directed to methods of forming a compoundmetasurface element comprising forming two layers of metasurfacefeatures atop a substrate, wherein the two layers are offset from eachother by a distance smaller than or on the same order as the wavelengthof light within the specified operational bandwidth such that the twolayers of metasurface features operate in conjunction to impose a phaseshift on impinging light.

Additional embodiment are directed to methods of forming a metasurfaceelement including:

-   -   forming a plurality of identical or unique first metasurface        elements;    -   providing a plurality of identical or unique illumination        sources disposed in a planar array and integrating at least one        of the plurality of first metasurface elements with each of the        plurality of illumination sources in the array such that light        from each of said plurality of illumination sources passes        through at least one of the first metasurface elements and an        angular deflection is imposed thereby;    -   disposing a first spacer layer between the planar array of        illumination sources and the first metasurface elements, the        first spacer layer being configured to create divergence in        light emitted from each of the illumination sources of the        planar array prior to impinging on the respective first        metasurface element,    -   disposing a second metasurface element at a distance from the        plurality of first metasurface elements, the second metasurface        element configured to imprint a far-field illumination pattern        onto a light field formed by the emission of all of the        plurality illumination sources; and    -   disposing a second spacer layer between the first and second        metasurface elements such that an offset distance is formed        therebetween.

In additional other embodiments, at least the first spacer layercomprises a solid-state material.

In additional other embodiments, at least the second spacer layercomprises an air gap.

In still additional other embodiments, the plurality of metasurfacefeatures are inhomogeneous.

In yet additional other embodiments, the plurality of metasurfacefeatures diverge from an ideal shape by a pre-determinable amount basedon the dimensions of the metasurface features.

In still yet additional other embodiments, the method further includes:

-   -   forming a plurality of identical or unique first metasurface        elements;    -   providing a plurality of identical or unique sensor elements        disposed in a planar array and integrating at least one of the        plurality of first metasurface elements with each of the        plurality of sensor elements in the array such that light        impinging on each of said plurality of sensor elements passes        through at least one of the first metasurface elements and an        angular deflection is imposed thereby;    -   disposing a first spacer layer between the planar array of        sensor elements and the first metasurface elements, the first        spacer layer being configured to create convergence in light        impinging on each of the first metasurface elements of prior to        impinging on the respective sensor elements of the planar array;    -   disposing a second metasurface element at a distance from the        plurality of first metasurface elements, the second metasurface        element configured to imprint a far-field illumination pattern        onto a light field impinging thereon; and    -   disposing a second spacer layer between the first and second        metasurface elements such that an offset distance is formed        therebetween.

Numerous other embodiments are directed to methods of forming ametasurface element including:

-   -   forming a plurality of identical or unique first metasurface        elements;    -   providing a plurality of identical or unique sensor elements        disposed in a planar array and integrating at least one of the        plurality of first metasurface elements with each of the        plurality of sensor elements in the array such that light        impinging on each of said plurality of sensor elements passes        through at least one of the first metasurface elements and an        angular deflection is imposed thereby;    -   disposing a first spacer layer between the planar array of        sensor elements and the first metasurface elements, the first        spacer layer being configured to create convergence in light        impinging on each of the first metasurface elements of prior to        impinging on the respective sensor elements of the planar array;    -   disposing a second metasurface element at a distance from the        plurality of first metasurface elements, the second metasurface        element configured to imprint a far-field illumination pattern        onto a light field impinging thereon; and    -   disposing a second spacer layer between the first and second        metasurface elements such that an offset distance is formed        therebetween.

Several embodiments are directed to metasurface elements including:

-   -   an array of metasurface features disposed atop a substrate        transparent to light over a specified operational bandwidth, the        array comprising a plurality of metasurface features having        feature sizes smaller than the wavelength of light within the        specified operational bandwidth and configured to impose a phase        shift on impinging light within the plane of plurality of        metasurface features;    -   wherein the plurality of metasurface features are inhomogeneous,        and diverge from an ideal shape by a pre-determinable amount        based on the dimensions of the metasurface features.

In several other embodiments, the ideal shape is a square, and where theideal square has a side dimension of less than 200 nm the metasurfacefeatures are formed as circles, and where the ideal square has a sidedimension of less than 300 nm the metasurface features are formed assquares having rounded edges.

Many embodiments are directed to metasurface enabled illumination orsensor arrays including:

-   -   a plurality of identical or unique illumination sources or        sensor elements, arranged in a planar array;    -   a first spacer layer disposed above the planar array of        illumination sources and configured to create divergence in        light emitted from each of the illumination sources of the        planar array or convergences in light impinging on each of the        sensor elements;    -   a plurality of identical or unique first metasurface elements        disposed above the first spacer layer, at least one of the        plurality of first metasurface elements being associated with        each of the plurality of illumination sources or sensor elements        in the array such that light emitted from each of the plurality        of illumination source or impinging on each of said plurality of        sensor elements passes through at least one of the first        metasurface elements and an angular deflection is imposed        thereby;    -   a second metasurface element disposed at a distance from the        plurality of first metasurface elements, the second metasurface        element configured to imprint a far-field illumination pattern        onto a light field impinging thereon; and    -   a second spacer layer between the first and second metasurface        elements such that an offset distance is formed therebetween.

In many other embodiments, the plurality of metasurface features on eachof the metasurface elements are inhomogeneous, and diverge from an idealshape by a pre-determinable amount based on the dimensions of themetasurface features.

In still many other embodiments, the plurality of metasurface featureson at least the first or second metasurface element are configured tohave an asymmetric cross-section and are disposed at least two differentangles of rotation such that the metasurface element is configured toimprint at least two patterns having orthogonal polarization and beinglinearly offset one from the other on the illumination sources or detectsuch patterns from the impinging light prior to illumination of thesensor elements, the array being configured such that three-dimensionalinformation is obtained from a scene by the array in a single-shot.

In yet many other embodiments, the illumination sources are polarized orunpolarized, and selected from the group consisting of: VCSELs,solid-state laser, quantum cascade laser, LED, and superluminescent LED.

In still yet many other embodiments, the two patterns are unique.

In still yet many other embodiments, the two patterns have at least50,000 combined points.

In still yet many other embodiments, at least a first pattern isconfigured to obtain a measurement of the foreground of the scene, andwherein at least a second pattern is configured to obtain a measurementof the background of the scene.

In still yet many other embodiments, the two patterns are diagonallypolarized relative to the laser polarization.

In still yet many other embodiments, more than two patterns having morethan two different polarizations are used.

Various embodiments are directed to metasurface element enabled sensorsincluding:

-   -   at least one sensor element;    -   at least one first and at least one second metasurface element        disposed at an offset distance above the at least one sensor        element, and having a first spacing layer disposed therebetween;    -   wherein each of the at least one first and second metasurface        elements comprise an array of metasurface features disposed atop        at least one substrate transparent to light over a specified        operational bandwidth, the array comprising a plurality of        metasurface features having feature sizes smaller than the        wavelength of light within the specified operational bandwidth        and configured to impose a phase shift on impinging light within        the plane of plurality of metasurface features; and    -   wherein the arrays of metasurface features on each of the at        least one first and second metasurface elements are configured        to gather light of a specified operational bandwidth across a        specified field of view and shift the incoming light such that        it impinges the sensor element at a zero or near-zero degree        critical ray angle.

In various other embodiments, the first spacing layer is one of either asolid-state spacer material or an air gap.

In still various other embodiments, the field of view is ±44 degrees.

In yet various other embodiments, the sensor further includes a narrowbandwidth optical filter disposed between the metasurface elements andthe sensor element.

In still yet various other embodiments, the narrow bandwidth opticalfilter is comprised of alternating layers with a low index of refractionand high index of refraction selected from the group consisting ofsilicon dioxide, titanium dioxide, amorphous silicon, silicon nitrideand aluminum oxide.

In still yet various other embodiments, the sensors further include aplurality of identical microlenses disposed between the metasurfaceelements and the sensor element.

In still yet various other embodiments, the at least one firstmetasurface element and at least one second metasurface elements aredisposed on opposite sides of the same substrate, and wherein thesubstrate comprises the first spacing layer.

In still yet various other embodiments, the two metasurface elements oneither side of the substrate have the same height.

In still yet various other embodiments, the two metasurface elements areformed from a film deposited simultaneously on the front surface andback surface of the same substrate using a conformal deposition processselected from the group of pressure chemical vapor deposition and atomiclayer deposition.

In still yet various other embodiments, the at least one firstmetasurface element and at least one second metasurface elements aredisposed facing inward toward each other on separate substratesseparated by an air gap.

In still yet various other embodiments, the sensors further include anoptical bandpass filter integrated into the outward facing surface ofthe substrate of the at least one second metasurface.

In still yet various other embodiments, the sensors further include atleast third metasurface element disposed between the first and secondmetasurface elements and the CMOS sensor and configured to angularlydiverge the path of the incoming light such that the light impinging onthe CMOS sensor has a non-zero chief ray angle.

In still yet various other embodiments, the at least three metasurfacesare configured to minimize grid distortion to less than 5% over thespecified field of view.

In still yet various other embodiments, the sensor element is a CMOSsensor.

Further embodiments are directed to a metasurface element enabled singleplatform imaging/sensing system including:

-   -   at least one sensor element and at least one illumination        source;    -   at least one separate metasurface element disposed at an offset        distance above each of the at least one sensor element and at        least one illumination source, and having at least one spacing        layer associated with each respectively;    -   wherein each of the metasurface elements comprise an array of        metasurface features disposed atop a substrate transparent to        light over a specified operational bandwidth, the array        comprising a plurality of metasurface features having feature        sizes smaller than the wavelength of light within the specified        operational bandwidth, and wherein the at least one illumination        metasurface element disposed in association with the        illumination source is configured to impose a radiation pattern        on a light field emitted therefrom within the plane of plurality        of metasurface features, and wherein the at least one sensor        metasurface element disposed in association with the at least on        sensor element is configured to detect the radiation pattern of        the light field after the illumination of a scene.

In still further embodiments, the system further includes a plurality ofseparate metasurface elements and spacer layers associated with each ofthe illumination source and the sensor element.

In yet further embodiments, the metasurface elements associated with theillumination source imprint two orthogonal polarizations on the lightfield to produce at least two patterns having orthogonal polarizationand being linearly offset one from the other on the light fieldilluminating the scene, and wherein the metasurface elements associatedwith the sensor element are configured to detect the at least twopatterns such that three-dimensional information about the scene can begathered.

Numerous embodiments are directed to methods for fabricating ametasurface element for imprinting a desired far-field intensity on anillumination source including:

-   -   calculate an illumination source far field;    -   calculate a target far field, wherein the target is a        metasurface element;    -   calculate a least-squares fit to the target far field to obtain        a pseudo far field such that the convolution of the pseudo far        field and the illumination source far field yields the target        far field;    -   set the initial metasurface feature array grid and phase to an        initial condition;    -   determine one or more objective cost functions and calculate a        gradient function for each of the one or more cost functions for        each of a plurality of pixels of the metasurface element;    -   input a result from the one or more cost functions and the        gradient function into an optimization algorithm;    -   update the phases for each of the plurality of pixels of the        metasurface element and repeat gradient calculation and        optimization until the objective cost function converges; and    -   output a calculated metasurface element phase profile.

In numerous other embodiments, the cost function is selected from thegroup consisting of: squared distance from target, nearest neighbordistance, squared error of the far field projection of the metasurfaceelement under illumination, and smoothness of calculated far field.

In still numerous other embodiments, the optimization algorithm is oneof either conjugate gradient or L-Broyden-Fletcher-Goldfarb-Shannon.

Several embodiments are also directed to methods of forming ametasurface element on a substrate comprising a plurality of metasurfacefeatures having feature sizes smaller than the wavelength of lightwithin the specified operational bandwidth and configured to impose aphase shift on impinging light within the plane of plurality ofmetasurface features, wherein the substrate has a substrate thicknessunsuitable for use with a target optical system at and further includingat least one of the following:

-   -   removing at least a portion of the backside of the substrate        through one or both grinding or chemical etching; and    -   aligning and fusing an additional substrate to the substrate of        the metasurface element.

In several other embodiments, the additional substrate itself has ametasurface element disposed on one surface thereof, and wherein thesubstrate and additional substrate are fused along surface opposite thesurfaces on which the relative metasurface elements are disposed.

In still several other embodiments, the method of fusing uses a bondingprocess having a thermal budget below 600° C.

In yet several other embodiments, the bonding process is a wafer bondingprocess using an adhesive selected from the group of an optical epoxy,benzocyclobutene, a UV cured polymer, SU8, and a plasma activate silicondioxide film.

In still yet several other embodiments, the methods further includeremoving at least a portion of the backside of one or both of thesubstrates prior to fusing.

In still yet several other embodiments, the methods further includeforming at least a first metasurface element on a first side of a firstsubstrate, and forming at least a second metasurface element on a firstside of a second substrate, and fusing the first and second substratestogether along sides opposite the first sides of said substrates using abonding process having a thermal budget below 600° C.

In still yet several other embodiments, the plurality of metasurfacefeatures are inhomogeneous.

In still yet several other embodiments, the plurality of metasurfacefeatures diverge from an ideal shape by a pre-determinable amount basedon the dimensions of the metasurface features.

In still yet several other embodiments, the methods further include:

-   -   embedding and planarizing at least one of the first and second        metasurface elements;    -   forming at least a third metasurface element on a first side of        a third substrate; and    -   fusing the side of the third substrate opposite the first side        to the planarized first or second metasurface using a bonding        process having a thermal budget below 600° C.

In still yet several other embodiments, the planarization furthercomprises embedding at least one of the first and second metasurfaceelements in one of either a polymer or a solid-state bonding agent.

In still yet several other embodiments, including iterating the steps offorming, embedding, and fusing to form a layered stack of four or moremetasurface elements.

In still yet several other embodiments, at least one of layers of at oneend of the layered stack is one of either an illuminator or a sensor.

In still yet several other embodiments, the methods further include:

-   -   inserting a spacer substrate between the sides of the first and        second substrates opposite the metasurface elements, the spacer        substrate having at least one aperture disposed therethrough;        and    -   fusing the spacer substrate to the first and second substrates        using a bonding process having a thermal budget below 600° C.,        such that the at least one aperture forms an air gap between the        first and second substrates.

Numerous other embodiments are directed to a metasurface elementincluding:

-   -   an array of metasurface features disposed atop a substrate        transparent to light over a specified operational bandwidth, the        array comprising a plurality of metasurface features having        feature sizes smaller than the wavelength of light within the        specified operational bandwidth and configured to impose a phase        shift on impinging light within the plane of plurality of        metasurface features, and wherein the plurality of metasurface        features are formed from one of the group consisting of:    -   amorphous-Si metasurface features embedded in SiO₂ having a        pillar height from 500 to 1000 nm and a pillar diameter from 100        to 300 nm;    -   amorphous-Si metasurface features embedded in SiO₂ having a        pillar height of 600 nm and a pillar diameter from 100 to 300        nm;    -   amorphous-Si metasurface features having air gaps disposed        therebetween and having a pillar height from 1 to 500 nm and a        pillar diameter from 100 to 350 nm;    -   amorphous-Si metasurface features having air gaps disposed        therebetween and having a pillar height from 480 nm and a pillar        diameter from 100 to 280 nm;    -   TiO₂ metasurface features having air gaps disposed therebetween        and having a pillar height from 300 to 1000 nm and a pillar        diameter from 100 to 350 nm;    -   TiO₂ metasurface features having air gaps disposed therebetween        and having a pillar height of 975 nm and a pillar diameter from        100 to 300 nm;    -   amorphous-Si metasurface features embedded in benzocyclobutane        and having a pillar height of 590 nm and a pillar diameter from        100 to 300 nm;    -   amorphous-Si metasurface features embedded in SiO₂ and having a        pillar height of 600 nm and a pillar diameter from 100 to 275        nm;    -   amorphous-Si metasurface features embedded in SU8 and having a        pillar height of 675 nm and a pillar diameter from 100 to 300        nm; and    -   amorphous-Si metasurface features in air and having a pillar        height of 600 nm and a pillar diameter from 100 to 300 nm with        an element spacing of 450 nm.

In numerous other embodiments where amorphous-Si is the material ofchoice, the amorphous Si may be hydrogenated resulting in higher opticaltransmission as compared to amorphous silicon where hydrogen is notpresent in the structures.

Additional embodiments and features are set forth in part in thedescription that follows, and in part will become apparent to thoseskilled in the art upon examination of the specification or may belearned by the practice of the disclosure. A further understanding ofthe nature and advantages of the present disclosure may be realized byreference to the remaining portions of the specification and thedrawings, which forms a part of this disclosure.

BRIEF DESCRIPTION OF THE DRAWINGS

The description will be more fully understood with reference to thefollowing figures, which are presented as exemplary embodiments of theinvention and should not be construed as a complete recitation of thescope of the invention, wherein:

FIGS. 1A to 1G provides schematics illustrating a fabrication processfor metasurface elements in accordance with embodiments of theinvention.

FIG. 2A provides a schematic illustrating an embedded metasurfaceelement with anti-reflection coatings in accordance with embodiments ofthe invention.

FIG. 2B provides a schematic illustrating a planarized-embeddedmetasurface element with anti-reflection coatings in accordance withembodiments of the invention.

FIG. 3 provides a schematic flowchart illustrating a process forfabricating metasurface elements in accordance with embodiments of theinvention.

FIG. 4A to 4C provide schematics of a metasurface element havingfeatures of varying cross-section in accordance with embodiments of theinvention.

FIG. 5 provides a schematic illustrating the combination of multiplesubstrates having metasurface elements in accordance with embodiments ofthe invention.

FIG. 6 provides a schematic illustrating the combination of multiplesubstrates having multiple metasurface elements in accordance withembodiments of the invention.

FIG. 7 provides a schematic illustrating the combination of multiplesubstrates having multiple metasurface elements incorporating an air gapin accordance with embodiments of the invention.

FIG. 8A provides a schematic illustrating metasurface elementsincorporating spacers integrated with a sensor/illuminator component inaccordance with embodiments of the invention.

FIG. 8B provides a schematic illustrating metasurface elementsincorporating spacers in accordance with embodiments of the invention.

FIG. 9 provides a schematic illustrating a multiple metasurface elementsubstrate in accordance with embodiments of the invention.

FIG. 10A provides a flowchart for using metasurface elements to producean arbitrary radiation pattern out of a VCSEL or VCSEL array inaccordance with embodiments of the invention.

FIGS. 10B and 10C provide diagrams of phase (10B) and intensity (10C)obtained using the process of FIG. 10A in accordance with embodiments ofthe invention.

FIG. 11 provides a schematic illustrating an array metasurface elementcoupled with a set of pixelated sensor elements or illumination sourcescombined with a second metasurface into an integrated package inaccordance with embodiments of the invention.

FIGS. 12A to 12C provide schematics illustrating a polarizationsplitting metasurface element producing two unique radiation patternsout of a VCSEL array in accordance with embodiments of the invention.

FIG. 13 provides a schematic illustrating a two metasurface elementcombined with a second element such as a cut filter where thechief-ray-angle of the focused light is 0 degrees with respect to thefilter plane in accordance with embodiments of the invention.

FIG. 14 provides a schematic illustrating a two metasurface elementsystem where each metasurface element is formed on a unique substrate inaccordance with embodiments of the invention.

FIG. 15 provides a schematic illustrating a three metasurface elementsystem designed to correct for multiple monochromatic aberrations inaccordance with embodiments of the invention.

FIG. 16 provides a schematic illustrating the chief ray angle at theimage sensor plane as a function of image height for the metasurfaceelement system of FIG. 15 in accordance with embodiments of theinvention.

FIG. 17 provides a schematic illustrating an example of grid distortionfrom the metasurface element system of FIG. 15 in accordance withembodiments of the invention.

FIG. 18 provides a schematic illustrating an integrated system withmetasurface elements on the illuminators and detectors in accordancewith embodiments of the invention.

FIG. 19 provides a schematic illustrating an integrated system withmetasurface elements on the illuminators and detectors where thepolarization of light provides an extra degree of freedom in accordancewith embodiments of the invention.

FIG. 20 provides data graphs showing the phase and transmission responseof metasurface features comprising cylindrical pillars composed ofamorphous silicon embedded in SiO₂ in accordance with embodiments of theinvention.

FIG. 21 provides data graphs showing the phase and transmission responseof metasurface features comprising cylindrical pillars composed ofamorphous silicon in air in accordance with embodiments of theinvention.

FIG. 22 provides data graphs showing the phase and transmission responseof metasurface features comprising cylindrical pillars composed ofamorphous TiO₂ in air in accordance with embodiments of the invention.

FIG. 23 provides data graphs showing the phase and transmission responseof metasurface features comprising cylindrical pillars composed ofamorphous silicon encapsulated in polymer for a wavelength of 850 nm inaccordance with embodiments of the invention.

FIG. 24 provides data graphs showing the phase and transmission responseof metasurface features comprising cylindrical pillars composed of Siencapsulated in SiO₂ for a wavelength of 850 nm in accordance withembodiments of the invention.

DETAILED DESCRIPTION OF THE INVENTION

Turning now to the drawings, metasurface elements, integrated systemsincorporating such metasurface elements with light sources and/ordetectors, and methods of the manufacture and operation of such opticalarrangements and integrated systems are provided. Many embodiments aredirected to systems and methods for integrating transmissive metasurfaceelements with other semiconductor devices or additional metasurfaceelements, and more particularly to the integration of such metasurfaceswith substrates, illumination sources and sensors. In some embodiments,the metasurface elements may be used to shape output light from anillumination source or collect light reflected from a scene to form twounique patterns using the polarization of light. In such embodiments,shaped-emission and collection may be combined into a single co-designedprobing and sensing optical system.

In many embodiments, metasurface elements may incorporate multi-layermetasurface elements comprising combinations of two or more metasurfaceoptical elements. In various such embodiments the multi-layermetasurface elements may be free-standing (i.e., not directly integratedwith a specific illuminator or sensor into a system). In some suchembodiments, the optical system may consist of a single physicalcomponent or substrate having metasurface elements disposed on eitherside thereof. In some embodiments, multiple substrates having multiplemetasurface elements may be combined to make more complex systems. Insuch embodiments, the thickness of the substrate may be determined bythe requirements of the optical system, manufacturing constraints andthe specific designs of the two metasurfaces. In various embodiments,the multi-layer metasurface elements may be formed by patterning eachindividual metasurface element on unique substrates and subsequentlyfusing the substrates together through a suitable technique, e.g., waferbonding, optical adhesive. In general, however, in accordance withembodiments any number of metasurface elements may be combined throughany number of steps using CMOS or related processes.

In many embodiment, the metasurface elements may be free standing or maybe embedded within another material. In various such embodiments, theselection of the embedding material includes the appropriate selectionof refractive index and absorption characteristics. In many suchembodiments, the embedding material may provide mechanical stability andprotection as well as an additional design degree of freedom thatenables the metasurface to perform a desired optical function.

In various embodiments, the metasurface elements may be directly mountedor fabricated on an LED, VCSEL facet or each facet of a VCSEL in anarray to minimize device thickness and optimizemetasurface-illuminator/sensor alignment. In some such embodiments theresultant system can be used to convert a natural Lambertian or somearbitrary light distribution to a broad range and essentially arbitrarylight distribution including, for example, a so-called top hat, aso-called bat-wing profiles, or any other desired structured lightpattern.

In some embodiments, a spacing layer of a defined thickness (e.g., theworking distance) may be deposited on the CMOS image sensor, LED, VCSEL,etc., to implement an optical distance appropriate for a desired cameradesign, illuminator design or optimal system performance. In varioussuch embodiments, the spacing layer material may be organic or inorganicand may have a lower refractive index than the dielectric elementscomprising the metasurface. In some such embodiments, the thickness ofthe spacing layer may be modified to provide appropriate optical spacingfor the specific optical system.

Various embodiments are also directed to methods of fabricatingmetasurface elements. In some such embodiments, methods are directed tothe manufacture of metasurface elements on a wafer incorporating otherdevices, such as sensors or illuminators, thereby avoiding, in someembodiments, expensive manufacturing processes, such as, for example,the mechanical assembly of small dimension elements, or the activealignment of optics with sensors. In some such embodiments, metasurfaceelements may be integrated with the sensor (or the illuminator) in aseries of operations at a semiconductor fab. In many such embodiments asequence may include: (i) sensor or illuminator, (ii) optional microlensarray/collimator, optional filter, optional spacing layer, optionalmetasurface element(s), optional additional spacing layer, optionalmetasurface element(s), optional anti-reflection (AR) layer, optionalprotection layer. In many such embodiments a sequence of elements mayinclude: (i) sensor or illuminator, (ii) optional microlensarray/collimator, optional filter, optional spacing layer, optionalmetasurface element(s), optional additional spacing layer, optionalmetasurface element(s), optional anti-reflection (AR) layer, optionalprotection layer.

Embodiments for Manufacturing Metasurface Elements

Currently the manufacture of metasurface elements requires the use ofspecialized processes and systems that are incompatible to massmanufacturing limiting the implementation and adoption of suchmetasurface elements in CMOS devices. An exemplary description of aconventional process for forming metasurface elements can be found, forexample, in U.S. Pat. No. 8,848,273, the disclosure of which isincorporated herein by reference. The capability to produce metasurfacesvia standard semiconductor processes, would enable direct integration ofmetasurface optics with functional elements such as light emittingdiodes (LEDs), vertical cavity surface emitting laser (VCSEL),complimentary metal-oxide-semiconductor (CMOS) image sensors,micro-electromechanical (MEMs) devices, etc., where direct integrationmeans combination of a metasurface element and sensor/illuminator usingunit processes identical or similar to those used to make the functionalCMOS elements.

Accordingly, many embodiments are directed to methods for thefabrication of metasurface elements and systems, and more particularlyto methods that are capable of being implemented within a conventionalsemiconductor foundry. In various embodiments, conventional processesadapted for the manufacture of metasurface elements may includephotolithography, nanoimprinting, various chemical vapor deposition(CVD), atomic layer deposition (ALD) and physical vapor deposition (PVD)mass transfer processes, and chemical and plasma etching (and CMC),among others. Turning to the figures, an exemplary set of fabricationprocesses tailored for the manufacture of various aspects of embodimentsof metasurface elements is presented in the schematic of FIGS. 1A to 1G.

Metasurface optical elements are comprised of dielectrics with featuresizes from 10's of nanometers to micron scale, or generally smaller thanthe wavelength of light at which the metasurface is being used.Referring to FIGS. 1A to 1C, in many embodiments, an initial step tomanufacturing metasurface elements comprises the patterning andformation of an array of metasurface features. In many such embodiments,as shown in FIG. 1A, this metasurface feature formation process isaccomplished by depositing a patterning material (14) on top of anappropriate hard mask material (12) of thickness t (t being thethickness of the film and the height of the final metasurface) thatitself is disposed atop a suitable substrate (10). Any suitabledeposition technique may be used to form these layers, including, forexample, sputtering, chemical vapor deposition (CVD) or atomic layerdeposition (ALD).

Although throughout this disclosure exemplary materials will bediscussed in relation to specific embodiments, it will be understoodthat any suitable combination of patterning material, hard maskmaterial, and substrate may be used for these purposes. For example, invarious embodiments, the substrate material is selected to providesuitable structural support and to be transparent to light over adesired bandwidth. Exemplary substrate materials that have beensuccessfully implemented using the processes described in embodimentsinclude, for example, fused silica, sapphire, borosilicate glass andrare-earth oxide glasses. Similarly, the hard mask material may bechosen from any readily available material suitable for use insemiconductor foundries. Exemplary hard mask materials include, forexample, silicon, silicon nitride of various stoichiometries, silicondioxide, titanium dioxide, alumina etc. In various embodiments, such as,for example, where the hard mask material forms an embedding material(as described in greater detail below) the hard mask material may bechosen to have a low (e.g., from 1 to 2.4) refractive index at aspecific wavelength of light. Finally, the patterning material inaccordance with embodiments may be formed of any suitable photoresist,such as, for example, a photoresist tuned for a lithographic wavelengthcapable of forming metasurface features of a desired size. Exemplarylithographic processes include, for example, ultraviolet and deepultraviolet (DUV) lithography. In other embodiments, the patterninglayer may be a polymer material suitable for use in nanoimprintlithography. Independent of the specific material used, the patterningmaterial must be capable of reproducing a desired pattern of featuresfrom 10's of nanometers to micron scale, and must suitably protect theunderlying hard mask film in selective areas in subsequent steps.

In particular, as shown in FIG. 1B, once the substrate (10), hard mask(12) and patterning material (14) layers are in place, the patterningmaterial is patterned to reproduce an array of features (16)corresponding to either a negative or positive reproduction of the finalintended metasurface feature array structure. The process of producingthis feature array pattern can take any form suitable to produce thedesired feature sizes. For example, in embodiments of metasurfaceelements for use in visible or near-IR applications UV lithography(e.g., where the wavelength of operation of the UV lithography step isbelow 193 nm) may be used. In still other embodiments, patterns may beimprinted physically by a master stamp in a nanoimprint lithographyprocess.

As shown in FIG. 1C, once the desired feature array pattern (16) is inplace, an anisotropic etch process is used to transfer the desiredfeature pattern into the hard mask layer (12). An exemplary anisotropicetch process for use in accordance with embodiments is reactive ionetching process. It will be understood that a number of possiblechemistries may be used in the reactive ion etching process including,for example, SF₆ gas, Cl₂ gas, BCl₃ gas, C₄F₈ or any mixture of thesegases. Further, the gas mixture may be static or timed in a multiplexedmanner where one or more of the gasses is introduced followed after someset time period by a second unique set of one or more of the gases.Regardless of the specific anisotropic etch process used, once thepattern is etched into the hard coat layer the remaining photoresist maybe removed using any suitable method (e.g., chemical solvent, chemicaletchant, plasma etchant, etc.). Note, in various embodiments it may bedesirable to use the feature array (16) formed in the hard mask material(14) as the final metasurface element. In such embodiments, the processcan be stopped here, or combined with the deposition of suitable ARcoatings or mechanical protection embedding layers as described, forexample, in FIG. 1G.

As shown in FIG. 1D, where a specific metasurface material is to be usedin the final metasurface element, the feature pattern (16) formed in theetched hard mask (12) (as described above in FIG. 1C) can act as atemplate for the final metasurface structure. In such embodiments, aseparate metasurface material (18) is deposited using a suitableconformal coating method such as chemical vapor deposition (CVD), atomiclayer deposition (ALD), etc., to fill the mask negative and produce themetasurface element. As shown the metasurface material (18) overfillsthe spaces formed by the feature pattern (16) etched in the hard mask(12) to completely fill the voids. In addition to filling the voids(20), this process leaves an over-layer of the metasurface materialabove the remaining hard mask. Again, although specific metasurfacematerials will be discussed throughout, it will be understood thatmetasurface materials in accordance with embodiments may be chosen fromany readily available dielectric material having a desired refractiveindex and suitable for use in semiconductor foundries. Exemplarymetasurface materials include, for example, silicon, silicon nitride ofvarious stoichiometries, silicon dioxide, titanium dioxide, alumina etc.

Referring to FIG. 1E, once the overfill of metasurface material (18) isdeposited, an etch or chemical-mechanical planarization may be performedin accordance with embodiments to remove the overfill layer providing auniform height to the patterned hard mask (12) and metasurface material(12). In embodiments where an embedded metasurface is desired, and wherea suitable hard coat material has been chosen to act as the embeddingmaterial (as previously described) the process may be stopped and theresultant metasurface material embedded with hard coat materialstructure used as the final metasurface element. This metasurfaceelement may then be optionally coated with suitable AR coating layers ormechanical protection layers as described below.

In various embodiments, as shown in FIG. 1E, the hard mask material (12)is removed leaving behind free-standing metasurface elements (20). Insuch embodiments, the hard mask may be removed using a selective etchchemistry which etches the hard mask material (12) at a much higher ratethan the metasurface material (18) (e.g., 100:1 or 1000:1 or greater).As will be understood by those skilled in the art, such processes aredependent on the specific selection of metasurface material and hardmask material. For example, in embodiments where the hard mask issilicon and the metasurface is TiO₂, a XeF₂ etch chemistry willselectively remove the silicon while leaving the metasurface materialessentially unaltered. Note, in embodiments where the metasurfaceelement is designed to be freestanding, i.e., the metasurface elementfeatures protrude from the end of the substrate with only air gaps (22)separating them, the process is complete at this step.

Finally, as previously discussed, in certain embodiments where it isdesirable for the metasurface to have an AR coating or mechanicalprotection layer, additional steps are required to complete the finalmetasurface element. Referring to FIG. 1G, in various embodiments an ARcoating or mechanical protection or planarizing layer (24) may also bedeposited to file the voids (22) between the metasurface features (20)and extend above the surface of the metasurface material layer (18). Itwill be understood that any material having optical properties suitablefor a specific optical system design, such as, for example, a suitablerefractive index and minimal optical absorption at a desired wavelengthor over the bandwidth of interest (the planarizing layer can allow formultiple levels of metasurface elements for complex optics systems) maybe used in this process. As described above, in order to protect themetasurface and provide improved functionality the metasurfaceconstituent elements and substrate faces in many embodiments are coatedin one or more materials or layers of material. Referring to FIG. 2A, aschematic of an embedded metasurface is shown. As illustrated, themetasurface features (20), which can be any material with desiredoptical properties as described above, are embedded in an embeddingmedium (24) typically having a lower-index of refraction. Exemplaryembedding materials include, for example, poly(methyl methacrylate),SUB, benzocyclobutene, and/or a solid film such as: silicon dioxide,aluminum oxide, titanium dioxide, silicon nitride, hafnium oxide, zincoxide, or spin-on-glass. The low-index embedding medium encapsulates themetasurface features and may extend some thickness above the metasurfacefeatures. In such embodiments, the low-index medium may act as aprotective barrier to the metasurface elements (i.e., provide mechanicalstability). The embedding material may also provide an additional designdegree of freedom for the system that allows for certain properties tobe optimized, e.g., to improve the overall transmission or efficiency ofthe metasurface and in some instances obviate the need for a separate ARcoating. It is shown here that the embedded metasurface is fabricated ona substrate but the metasurface could also be extending from asensor/illuminator, as will be described in detail below. The combinedelement (metasurface, embedding medium and substrate) may also be coatedwith a suitable anti-reflection coating on the side of the substratecontaining the metasurface (26′) and/or on the backside of the substrate(26). In many embodiments, the AR coating may comprise alternatinglayers of any combination of silicon dioxide, titanium dioxide, aluminumoxide, silicon nitride, aluminum nitride, or amorphous silicon, whereeach has a thickness less than the wavelength of light within theoperational bandwidth of the metasurface. Additionally, as describedabove the embedding medium itself can potentially be used as ananti-reflection coating.

Although certain embedded metasurface embodiments are described above,in various other embodiments the metasurface can be embedded andplanarized, as shown in FIG. 2B. In such embodiments, the metasurfaceelements may be embedded in a suitable low-index material (as describedabove), and in an additional step, the embedding medium (24) is thenetched or planarized such that its height is commensurate with themetasurface elements (20). Optional anti-reflection coatings may also beincluded on either the bare substrate surface (26) or on the patternedmetasurface side (not shown).

Embodiments for Manufacturing Metasurface Elements On ConventionalSubstrates

Although the above discussion has described in detail manufacturingprocesses capable of forming a variety of free-standing or embeddedmetasurface elements using conventional CMOS fabrication techniques, inpractice it may not be possible to adapt conventional metasurfaceelements to allow for the economic production of metasurface elementsusing pre-existing equipment in foundries. For example, one of thedesign criteria used conventionally to tailor the optical properties ofa metasurface element is the substrate thickness. Varying this substratethickness provides the metasurface element designer another degree offreedom in obtaining desired optical properties However, thepre-existing equipment in most foundries have limitations that lead tospecific mechanical requirements on the substrate upon which themetasurface elements will be fabricated. For the case of standardsubstrate diameters within foundries, e.g., 200 mm and 300 mm, thethickness of the substrate is limited to 725 microns and 775 microns,respectively. These fixed substrate thicknesses, in turn, imposespecific requirements on the optical function, and therefore the design,of a metasurface formed on the substrate or a system of multiplemetasurfaces formed on such a substrate (in mass production there maybe, for example, 5,000 metasurfaces formed on a single die, or more).

Accordingly, many embodiments are directed to processes for tailoringthe fabrication of the metasurface element or system to the specificsubstrate thickness upon which the metasurface or metasurface system isbeing produced. For example, in various embodiments the phase shiftsthat need to be imparted by the metasurface elements to impart aspecific function to the overall optical component(s) will be specificto the substrate thickness upon which the elements are formed.Accordingly, in some embodiments the procedure for designing andfabricating the metasurface element comprises: (1) considering thedevice specifications of the metasurface element, (2) considering thethickness and optical properties (index of refraction and absorption) ofthe substrate on which the metasurface is being formed, (3) optimizingthe phase profile of the metasurface to obtain the desiredspecifications for the properties of the substrate, and (4) determiningthe thickness and in-plane dimensions of the metasurface elementsrequired to reproduce the phase profile.

Referring to FIG. 3, an exemplary process in accordance with producingmetasurfaces using standard substrate thicknesses is provided. As shown,following deposition of the metasurface material and lithographicpatterning and etching (as described in FIGS. 1A to 1G, above), if themetasurface layer is designed for the standard substrate thickness anadditional protective layer or AR coating may be disposed on themetasurface layer before being sent for further back end processing. Inmany such embodiments, back end processing may comprise singulating thethousands of metasurfaces formed across the substrate using a dicingprocess. Further, in embodiments where it is desirable to produce ametasurface that has a final substrate thickness different than thestandard thicknesses discussed above an additional step to alter thethickness of the underlying substrate may be performed. In suchembodiments, the metasurface would initially be formed on a standardsubstrate diameter (200 or 300 mm) with a thickness standard insemiconductor processes (725 or 775 micron, respectively), again tocoincide with industry standards. After initial definition of themetasurface on the standard thickness substrates, subsequent back endprocessing would then be performed to alter the substrate thickness.Suitable methods for altering the thickness of the substrate accordingto embodiments include, for example, grinding or combination of grindingand chemical processing to gradually remove substrate material. In suchembodiments, the final substrate thickness upon which the metasurfacehas been formed can be any value less than the starting standardthickness. Alternatively, if thicker substrate is required, twoindependent wafers each comprising any number of metasurfaces (1,000 to10,000 individual metasurfaces) can be combined in accordance withembodiments to achieve desired thickness via wafer-bonding processessuch that the final monolithic unit, with a set of metasurfaces oneither side, has a total thickness as required by the final design.Processes according to such embodiments may be carried out for eithertwo substrates with standard thicknesses, if the final thicknessrequired is 2 times the standard thickness, or it can be carried out fortwo substrates that have been thinned so that the final thickness of thecombined unit has any desired thickness. In such embodiments, the “backend processing” may comprise an additional wafer bonding step where eachof the individual substrates can be aligned to each other before beingcombined.

Embodiments for Manufacturing Metasurface Elements with Non-IdealFeatures

In conventional processes for designing metasurfaces, shape fidelityfrom the designed metasurface to the fabricated is often assumed to beeither a 1 to 1 correspondence or to be maintained to within some errorrange. This approach leads to metasurface arrays often being comprisedof a single set of shapes where one feature of that set of shapeschanges, e.g., circles with varying diameters across the metasurface.However, fabrication techniques used for potential mass production ofmetasurfaces e.g., UV lithography as detailed above, are generallyunable to carry-out faithful reproduction of certain geometrical shapes.As such, many embodiments are directed to metasurface elements andmetasurface fabrication processes where the function of the metasurfaceis reproduced using non-ideal and inhomogeneous shapes.

For example, FIG. 4A provides a cross-sectional schematic of anexemplary section of a metasurface where an inhomogeneous set of shapesis distributed across the metasurface. In this specific embodiment,square pillars are desired. However, after fabrication what is actuallyformed within a given metasurface are an array of squares with varyingside lengths (e.g., s₁), squares with rounded corners of varying radii,re and circles with varying radii r₁ or r₂. Specifically, the largerfeatures here are designed to be squares or squares with roundedcorners; however, as the side lengths of the squares are reduced belowsome minimum side length the squares become circles. In processesaccording to embodiments, manufacturing limitations are simulated oneach desired metasurface feature shape, and these non-ideal orinhomogeneous feature elements then used to determine the finalmetasurface element array structure.

For example, FIGS. 4B and 4C, provide diagrams illustrating thevariation of printed and designed patterns from a metasurface elementmask reticle. As shown, in embodiments for a designed square feature ofside 200 nm and period of 450 nm, the printed fabrication technique willactually replicate a circle of diameter 200 nm (FIG. 4B). By contrast,for a square feature of side 296 nm and spacing of 450 nm, thefabricated feature is a square with rounded corners (FIG. 4C).Accordingly, many embodiments of metasurface elements where squaremetasurface features are designed may be substituted with roundedsquares below ˜300 nm and circle below ˜200 nm to allow for the use ofindustrial standard CMOS replication techniques.

Embodiments for Manufacturing Multiple Metasurface Elements

As previously discussed, various embodiments are directed to methods forwafer bonding two substrates incorporating metasurface elementstogether. Such embodiments may be modified to allow for the facilefabrication of multiple metasurface elements, such as, for example,doublets and triplets (e.g., metasurface elements comprising two orthree separate metasurface feature arrays). In particular, although manywafer bonding processes exist each imposes a specific thermal budget onthe substrates being joined. Since many embodiments of metasurfaceelements use amorphous Si as the metasurface material, excess heating ofthe substrates can result in the crystallization of the Si. Accordingly,embodiments are presented that allow for the formation of metasurfacedoublets and triplets using low temperature processes, such as, forexample, using UV cured polymers (such as benzocyclobutane (BCB) or thelike), or plasma activated SiO₂ to allow for wafer bonding of two ormore metasurface elements at low temperature.

Referring to FIG. 5, a schematic for forming a metasurface doublet inaccordance with embodiments is shown. As illustrated, in many suchembodiments, a plurality of unique metasurface elements (30 & 32) arefabricated on two distinct substrates (34 & 36). The metasurfaceelements are then made into a combined system by fusing the bottom(e.g., the portion of the face of the substrate without any metasurfaceelements) of each unique substrate. As discussed above, the substratesmay be fused by wafer bonding techniques, optical epoxy, or any suitablemethod for combining the two unique elements into a single elementwithin the allowed thermal budget of the metasurface material used. Thebonding material (38) in many embodiments can be adhesives such asbenzocyclobutene, cured polymers SU8 or a silicon dioxide film thatfacilitates a glass bond. In cases where the thermal budget of themetasurface material is low (less than 600° C.) the silicon dioxide bondcan be a low temperature plasma-activated SiO₂ bond. Additionally,although not illustrated, the metasurfaces may be embedded as describedin the embodiments illustrated in FIGS. 2A and 2B. In addition, asdescribed in reference to FIG. 3, the thickness of the two substrates,which ultimately constitutes the total thickness of the space betweenthe metasurfaces, may additionally be altered to optimize certainproperties of the combined system.

Although the disclosure thus far has detailed embodiments incorporatingonly two metasurface elements, the process may be generalized to anynumber of metasurface elements. For example, certain applications mayrequire three or more metasurfaces to be combined into a monolithicunit. In such a case, two substrates comprising separate metasurfaceelements may form the initial uncombined units. An illustration ofexemplary embodiment of such a process is provided in FIG. 6. As shown,in many such embodiments, at least one of the metasurface substrates(40) has only one side patterned with a metasurface element (42) whilethe opposite side of the substrate can be completely unpatterned or mayalso include a bandpass filter (44) for a specific wavelength ofinterest. In such embodiments the filter may be formed of one or moresuitable materials, including, for example, alternating layers of lowindex of refraction and high index of refraction materials such assilicon dioxide, titanium dioxide, amorphous silicon, silicon nitride,and aluminum oxide. At least a second metasurface substrate (46) has twounique metasurface elements (48 & 50) on each face of the substrate(this second metasurface substrate may also have been formed through anintermediate bonding step of its own as described above in relation toFIG. 5). The metasurface substrates (40 & 46) are then made into acombined system by fusing the bottom (e.g., the portion of the face ofthe first substrate (40) without any metasurface elements with theportion of the face of the second substrate (46) containing one of thetwo metasurface elements (48 & 50)) of each unique substrate. Asdiscussed above, the substrates may be fused by wafer bondingtechniques, optical epoxy, or any suitable method for combining the twounique elements into a single element within the allowed thermal budgetof the metasurface material used. The bonding material in manyembodiments can be adhesives such as benzocyclobutene, cured polymersSU8 or a silicon dioxide film that facilitates a glass bond. In caseswhere the thermal budget of the metasurface material is low (less than600° C.) the silicon dioxide bond can be a low temperatureplasma-activated SiO₂ bond. This bonding material is disposed on orbetween the faces of the two substrates to be joined. In certainimplementations, various metasurface elements can be optionallyencapsulated (52 & 54) as outlined above. However, in many embodimentsfor the facilitation of a bonding process, at least the metasurfaceelement (48) proximal to either the bare substrate face or bandpassfilter (44) in the combined triplet device is embedded in a polymerand/or solid-state bonding agent (56).

While the above instances of combining metasurface elements have hadeach metasurface element separated by a solid substrate, in someembodiments each metasurface elements may instead be separated by an airgap. Referring to FIG. 7, a schematic of a metasurface doubletcomprising an air gap is illustrate. As shown, in many such embodiments,two or more metasurface elements (60 & 62) are formed on uniquesubstrates (64 & 66) using a suitable method, such as that describedabove in relation to FIG. 5. The unique metasurface elements are thencombined with a third substrate or spacer substrate (68) comprising oneor more apertures (70) etched to make a monolithic unit where the spacewithin the aperture between the metasurfaces is unfilled (i.e., suchthat an air gap is formed between the metasurfaces elements (60 & 62)).The space between the metasurfaces provides an additional design toolfor system-level optimization. For example, in many embodiments byadjusting the spacer wafer thickness one can implement a variety ofdifferent designs. In addition, in various embodiments, as also shown inFIG. 7, it is possible to add additional spacer substrates (72) toincorporate other system elements, such as illuminators and/ or sensors(74).

In embodiments incorporating such spacer substrates, any suitablesubstrate material may be used. For example, in many embodiments thespacer substrates may be any low-index material, such as, for example,polymer, SiO₂, glass, etc. In addition, in other embodiments the spacermaterial may be coated in black chrome. The metasurface elements mayalso be formed of any material, which has been optimized for a specificbandwidth, such as for example, silicon, TiO₂, alumina, metal, etc. Themetasurface elements may also be fabricated using such methods asdescribed in FIGS. 1A to 1G or using semiconductor fabrication processesin general.

The above embodiments described processes for combining two and threemetasurfaces; however, such embodiments may be extended beyond just twoor three metasurfaces. For example, by iterating on the steps describedabove in relation to FIGS. 5 to 7, embodiments allow for the stacking ofany number of metasurface elements. Referring to FIG. 8A, in variousembodiments a set of metasurfaces (80, 82, 84, etc.) and spacer layers(86, 88, etc.) may be directly integrated with an illuminator or sensor.In such embodiments, an optional spacer layer (90) is first formed on asensor/illuminator (92) through a suitable deposition process, asdescribed, for example, in relation to FIGS. 1A to 1G. Following thespacer layer (90), any number of metasurface elements (80 to metasurfacen+1) may be fabricated as needed to carry out a desired function. Eachsubsequent metasurface may also be separated by a spacer layer (86 tospacer n+1) and the thickness of each spacing layer may be varied asrequired by the optical design. As previously discussed, the spacerlayers in such embodiments may be any low-index material, e.g., polymer,SiO₂, glass. As also previously discussed, the metasurface elements insuch embodiments may also be any material, which has been optimized fora specific bandwidth, e.g., silicon, TiO₂, alumina, metal, etc. Themetasurface elements may be fabricated using such methods as describedin FIGS. 1A to 1G or using other suitable semiconductor fabricationprocesses in general.

Although the above description assumes integration with a sensor orilluminator (92), a set of metasurface elements and spacer layers canalso be iteratively fabricated on a substrate (90), as illustrated inFIG. 8B. As shown, in such embodiments, the process is as described inrelation to FIG. 8A, but rather than integrating the metasurface/spacerstack onto a sensor/illuminator (92), the stack is produced on astand-alone substrate (90). The combined substrate and stack inaccordance with such embodiments may then be integrated into an opticalsystem or be used as a stand-alone optical component.

Embodiments of Multilayer Metasurface Elements and Their Manufacture

While in the previously-detailed embodiments each metasurface element isdesigned to carry out a unique optical function in a larger opticalsystem and the metasurface elements are typically separated bymacroscopic distances (distances of 10 or more wavelengths), in variousembodiments a plurality of two layers of patterned material may beprovided at a distance to each other microscopic distances (e.g., atdistances to each other smaller than or on the same order as thewavelength of light) such that the layer in combination form a singlemetasurface element performing a single optical function. This may beparticularly advantageous where an optical function requiring verycomplex metasurface features is called for. Such complex features may bebeyond the capability of standard CMOS fabrication techniques tofabricate. In such cases, combinations of simple features disposed atmicroscopic distances in accordance with embodiments may be used toreplicate the optical functions of the complex features shapes.Referring to FIG. 9, a schematic of an embodiment of a metasurfaceelement comprising two layers of patterned materials separated by adistance, t_(offset), is provided. Although only a schematic for atwo-layer system is shown, it will be understood that any number of suchlayers may be provided so long as the distance t_(offset) is smallenough to allow for a combination of the optical functions of theplurality of layers. These feature layers may be formed and combinedusing any suitable combination of the fabrication steps set forth inrelation to FIGS. 1 to 8, above.

Embodiments for Incorporating Metasurface Elements with VCSELs

The techniques and processes of fabricating metasurface elements inaccordance with embodiments also directly enable their integration withillumination sources. Of particular interest is the combination ofmetasurface elements with VCSELs and VCSEL arrays. In general, atransmissive metasurface element can imprint an arbitrary phase profileon an electromagnetic wave to produce any radiation pattern in thefar-field. Fabrication techniques for the metasurface elements inaccordance with embodiments enable direct integration with a VCSEL,solid state laser, quantum cascade laser, LED, superluminescent LED orany solid-state light source.

VCSELs can be conceptualized as single- (or few-) mode lasers whichgenerate an approximately collimated beam of laser light at a singlewavelength. Often to generate sufficient power or spatial extent adevice will contain not one VCSEL, but a 2-dimensional array of VCSELs.This light has a distribution (or illumination) in real space and inangular space. Metasurfaces when properly co-designed and integratedwith a VCSEL array have the ability to transform both the real andangular space distribution of either a VCSEL or VCSEL array. Inparticular, pairing a metasurface element with a VCSEL allows themetasurface element to imprint an arbitrary radiation pattern on thesource (e.g., batwing, top hat, super-Gaussian, or other patterns knownin the art).

FIG. 10A presents a flow-chart of a process, in accordance withembodiments, for fabricating a metasurface to create any desiredfar-field intensity from a VCSEL array. To obtain the illumination inreal space, in accordance with embodiments, the VCSEL is assumed tooperate in the far-field regime. The VCSEL's characteristic far field(VCSEL-FF), from experimental data, is propagated to the surface underillumination, which in this case is a metasurface element as definedabove. In the case of a VCSEL array, the output from many VCSELs via(VCSEL-FF) is summed at the surface under an assumption of incoherenceto generate the illumination. This surface illumination then gives theintensity distribution at the metasurface element (I-MS). Every point atthis illuminated surface also has a distribution of angles of incidentlight on it, taken from the VCSEL far field angular distribution. In asimplifying case, it is possible in accordance with embodiments toconsider where all the illuminated points have this same VCSEL far fieldangular distribution, though each point has a slightly different angulardistribution.

To generate a metasurface element which takes into account thedistribution of angles at the metasurface element in the design, from atarget far-field distribution (TARGET_FF) embodiments of the processconstruct a pseudo-far-field (PSEUDO-FF) that has the property that theconvolution:

$\begin{matrix}{{\left( {\left( {{PSEUDO}\text{-}{FF}} \right)*\left( {{VCSEL}\text{-}{FF}} \right)} \right)\left( {x,y} \right)} = {\left( {{TARGET}\text{-}{FF}} \right)\left( {x,y} \right)}} & \left( {{EQ}.\mspace{14mu} 1} \right)\end{matrix}$

That is, in accordance with embodiments, the pseudo-far-field convolvedwith the VCSEL far-field reproduces the target far-field. In suchembodiments, the pseudo-far-field is calculated by fitting a curve tothe target function. Then (PSEUDO-FF) is used as the target (orobjective function) in the remainder of the process.

In various embodiments, the process proceeds by initializing themetasurface grid by discretizing it and setting the phases to someinitial condition. In many embodiments, a cost function is decided upon.In various embodiments, this is chosen to be the squared error of thefar field projection of the metasurface under VCSEL illumination to(PSEUDO-FF). In some embodiments, other objectives, such as thesmoothness of the result in the calculated far-field, can alsooptionally be set. For each objective, a corresponding gradient functionis also derived. This gradient function and the results of thecalculation of the cost function are then used in embodiments as aninput into an optimization algorithm in accordance with embodiment, andas summarized in FIG. 10A. The optimization algorithm, in accordancewith embodiments, updates the results of the pixel phases and continuesuntil the objective function meets some criteria (i.e., convergence).Upon convergence of the cost function, the required metasurface phaseprofile is output and a metasurface element design is chosen dependingon the wavelength and desired material (e.g., as described in detailbelow), and a physical design for the metasurface element may becreated.

Exemplary data plots showing the output of the process according toembodiments for phase (10B) and intensity (10C) after employing thealgorithm described above for an example case. As shown, in suchembodiments, the phase is encoded by the metasurface elements and theintensity profile on the right is produced after the laser source passesthrough the metasurface element and is projected into the far-field.Accordingly, using such a process it is possible to obtain predictiveperformance data for a proposed metasurface element under desiredoperating conditions and to illustrate ways of optimizing thatperformance by modifying aspects of the metasurface element design, suchas, for example, size, height and spacing of elements, etc.

Embodiments for Incorporating Metasurface Elements with IlluminationArrays

While the above processes have focused on integrating metasurfaceelements with a single illumination source, e.g., as shown in FIGS. 7and 8A, metasurface elements can also be integrated with a set ofpixelated and distributed sources. As illustrated in FIG. 11, variousembodiments may comprise a set of illumination sources, p₁, p₂, . . .p_(n) (while this is shown in 1 D, it will be understood that the systemcan be extended to a 2D array and in general the array need not beperiodically spaced) designed to illuminate a scene (110). Although eachilluminator may be identical, in many embodiments the character of eachilluminator may be generally unique. For example, each illuminator mayhave a different wavelength, bandwidth or may even output a uniquelydriven optical waveform. In specific applications, the array in FIG. 11may be an array of VCSELs. In other applications, there may be threecolors (e.g., red, green and blue) that are then repeated periodicallywithin the array. Because each illuminator comprising array may haveunique properties, it may also be advantageous to have an array ofmetasurface elements, each with uniquely designed properties. In suchembodiments, the metasurface array (100) may be offset from theilluminator array (102) by a spacer (104) (similar to FIG. 7 or 8B). Aspreviously discussed, the thickness of the spacer layer (104) willdepend on the specific design, but in many embodiments the thickness isconfigured to allow the light from the illumination sources to divergesufficiently before interacting with the metasurface array (100). Again,the function of each metasurface element in the array may be generallyunique but in certain embodiments, each metasurface element may providecollimation of the underlying illuminator pixel or each metasurfaceelement may act to further mix each underlying illuminator pixel.

In addition to the first metasurface array (100), various embodimentsmay incorporate a second metasurface element (106) to further shape theemitted light from the illuminator array (102). In various embodiments,the second metasurface element (106) is also offset by a second spacerlayer (108). Although this second spacer layer (108) is shown in FIG. 11as an air gap spacer, it will be understood that this spacer can also bea solid state material as in other embodiments as described above. Inmany embodiments, the first metasurface array (100) is configured tointroduce an additional angular divergence into the illuminator array(102) while the second metasurface element (106) imprints a specificfar-field radiation pattern onto the light field. In other embodiments,the second metasurface element (106) may also be formed of an array ofmetasurface elements, each with unique functionality. In all suchembodiments, the metasurface elements, and particularly the secondmetasurface elements in the system, may be designed using embodiments ofthe algorithm described in FIG. 10A. While in this particular case, thesystem has been described as an array of pixelated illuminators (102)shaped by the metasurface arrays/elements to illuminate a scene (110);the system can also be considered in the reverse. For example, thepixelated illumination sources may instead be pixels of a CMOS imagesensor and instead of light being projected onto a scene, the system maybe configured to collect light from a scene (110) and focus the lightdown to a pixel.

In all embodiments where the illumination source is a VCSEL, it isunderstood that the disclosures can also apply to an array of VCSELs(VCSEL array). In such a VCSEL array many individual aperture VCSELswith designable properties are combined on a single chip. Such VCSELarrays are used to increase the total output power of the illuminationsource. The array may consist of a one-dimensional row of individualVCSELs or 2D grid of individual VCSELs where in each case the specificproperties of the VCSELs (e.g., power, wavelength, aperture diameter,beam divergence etc.) and the arrangement of the individual VCSEL (e.g.,center-to-center distance, periodic or aperiodic spacing, etc.) can allbe freely chosen.

In the context of metasurface element integration, embodiments ofmetasurface elements with generally (but not necessarily) uniquelydesigned properties can be patterned on top of each individual VCSEL inthe array, utilizing any of the techniques outlined herein. For example,a metasurface may be fabricated directly on the facet of each individualVCSEL in the array or a suitable dielectric spacer may be deposited onthe VCSEL followed by the integration of the metasurface on top of thecombined dielectric layer and VCSEL. In such embodiments, themetasurfaces may provide a particular radiation pattern for each VCSELand the entire system (VCSEL properties, geometrical parameters andmetasurface-enabled radiation pattern) can be iteratively optimized fora specific set of performance parameters.

In various other embodiments, a dielectric material, with an index ofrefraction lower than that of the constituent VCSEL material may bedeposited and planarized such that a single metasurface can be patternedon top of the dielectric material. This contrasts with embodiments whereeach VCSEL in the array has a unique metasurface patterned on its facet.Again, in such embodiments the combined system may be optimized toachieve a desired performance. Finally, in all of the above embodiments,integration of a metasurface with a VCSEL array may be accomplishedusing wafer level optics processes. In such embodiments, the spacerlayer may be air rather than a solid dielectric, similar to the deviceshown in FIG. 7.

Embodiments for Incorporating Metasurface Elements into 3D Applications

In certain 3D structured light applications, a pseudo-random binaryarray (PSBA) is projected onto a scene. A typical PSBA is built bydiscretizing 2D space, for example, in a square grid. Each grid point inthe x-y plane can be characterized by a unique index (i,j), where i andj are integers. At each point (i,j) a pseudo-random algorithm is used todetermine whether the grid point has a dot (representing the binaryvalue of 1) or no dot (representing a binary value of 0).

Typically, a diffractive optical element (DOE) is used to convertincident laser light, for example from a VCSEL or VCSEL array into asingle dot pattern. Such conversion schemes rely only on two intensityvalues in the projected field (dot or no dot). However, in general it isdesirable to impart multiple patterns onto a single scene and for eachof the multiple patterns to exist on separable information channels(i.e., having two patterns projected from a single element onto a sceneand having a method for uniquely identifying each pattern at a sensorplane). In some schemes of 3D imaging, multiple patterns are projectedonto a scene at different time slices (temporal variation). Theseschemes use either multiple distinct illumination patterns or someactive element, such as a spatial light modulator, which can beelectrostatically tuned to alter the projected pattern at differentpoints in time. These schemes, however, do not allow single-shotacquisition, increase the complexity and therefore the cost of thesystem and tend to be substantially larger than an integrated laser/DOE.Accordingly, many embodiments are directed to metasurface elementsconfigured to provide single-shot acquisition for 3D structure lightapplications.

Referring to FIGS. 12A to 12C, exemplary embodiments of a metasurfaceelement (120) composed of a plurality of metasurface features (122) withan asymmetric cross-section (e.g., rectangular or elliptical), a fixedheight, and an axis of rotation are provided that are capable ofimprinting two unique dot patterns with two orthogonal polarizationsonto a illumination source (124). While this exemplary embodiments willbe discussed in reference to a laser of fixed polarization, embodimentsmay also be configured to operate on an unpolarized source (e.g., alight emitting diode (LED)), where the function of the metasurfaceelement would be to split the unpolarized light into two distinctpolarizations (as shown schematically in FIG. 12B) and imprint anydesired arbitrary pattern onto the projected light. Whatever theillumination source, in various embodiments, the metasurface elementscan be integrated with the illumination source, (e.g., LED, VCSEL, VCSELarray, etc.), in accordance with embodiments described in thisdisclosure. For example, referring to FIG. 12A, the metasurface element(120) may be fabricated on a substrate (126) of desired thickness andthen bonded, either with a spacer layer that is subsequently bonded tothe illumination source (124), bonded directly to the illuminationsource or the substrate upon which the metasurface elements are formedcan be subsequently diced into individual units and combined with thelaser source through back-end packaging. For various embodiments of 3Dimaging systems, the illumination source may be in the near infrared(NIR) (e.g., at wavelengths of 850 or 940 nm).

Regardless of the specific configuration and manufacture of themetasurface elements used, in such embodiments the metasurface elementsoperate by shaping not only intensity, but also the polarization of thelight emitted from an illumination source. Specifically, in addition tointensity variations, light also has a vector quantity known aspolarization. Given a polarized illumination source, it is possible todecompose the illumination polarization into a basis of two orthogonalpolarizations or channels. Due to the orthogonality of thesepolarization bases, any pattern imprinted on these differentpolarization channels can also be independently sensed through asuitable detector configured to separate these polarization channels.

As a specific example, consider the following case. For an illuminationsource (in this example a polarized illumination source such as a laser)that emits light in horizontal polarization, |H

, it is possible to decompose the output into two polarizationsaccording to the equation:

$\begin{matrix}{\left. H \right\rangle = \frac{\left. A \right\rangle + \left. D \right\rangle}{\sqrt{2}}} & \left( {{EQ}.\mspace{14mu} 2} \right)\end{matrix}$

where |A

and |D

in this example are diagonal and anti-diagonal linear polarizations(although it will be understood that any set of polarizations may beused in accordance with embodiments). In such a case, as shown in FIG.12C, the pattern of metasurface features (122) of the metasurfaceelement (120) disposed over the illumination source (124) is configuredsuch that it imprints a separate dot pattern (as shown in FIG. 12B) ontoeach of these two polarizations. In accordance with embodiments thesedot patterns may be unique for each polarization for clarity, as shownin the exemplary schematic of FIG. 12B, or they may be partiallyoverlapping. Regardless of the specific configuration of the dots,however, in embodiments these patterns are projected on the same regionof space (i.e., their grids have an identical spatial origin). Invarious embodiments, complimentary dot patterns may be used such thatfor every point that there is a dot in Pattern 1, there is the absenceof a dot in Pattern 2 and vice versa, however, this is not essential.Such complimentary dot pattern configurations have the advantage that ifa single dot (e.g., area) of a scene is lost during the capture, thereis a complimentary dot of separate polarization that may capture it,thus providing a certain redundancy. In addition, while two patterns ofdots on a square grid are described in relation to this specificexemplary embodiment, it should be understood that the projectedpatterns might be of any configuration having any suitable geometry andshape. Similarly, while a specific illumination polarization and numberof polarizations upon which that illumination polarization wasdecomposed have been described, it will be understood that anypolarization and any number of different polarizations may be used inaccordance with embodiments.

As described above, the embodiments operate as a result of theorthogonality of the polarization channels upon which each pattern isimprinted. Because of this orthogonality, the reflected light from agiven scene can be separated, by a suitable detector, to create multipleimages of the same scene, one with Polarization 1 corresponding toPattern 1 and one with Polarization 2 corresponding to Pattern 2, asshown in FIG. 12B. The net result is that embodiments of such a systemprovide two nominally independent measurements of the distorted patternreflected from the scene without the need for time multiplexing.Accordingly, embodiments of such a system can be used to providesingle-shot, multiple measurements in 3D imaging systems, thus reducingambiguities and increasing accuracy.

Typical pattern projection systems used in mobile devices, for example,have a limitation on the total number of points that they can projectonto a scene. This limitation arises from a combination of the number ofconstituent VCSELs in a VCSEL array (which is not alterable by anyoperation of the optic producing the pattern) and the ability of theoptic producing the structured light pattern to create multiple replicasof each VCSEL comprising the VCSEL array. In practical implementations,this limits the number of projected points in a pattern to a specificnumber, N (typically around 30,000). In accordance with embodiments ofthe polarization-dependent metasurface systems described above, since asingle metasurface element has the ability to create multiple completelyunique patterns for each orthogonal polarization, even within thelimitations stated above, the total number of dots in a given patterncan be doubled (e.g., 2N), leading in a typical system to as many as60,000 points in a single projected pattern. This doubling can beunderstood by examining the nature of the patterns. Conceptually, atypical projected pattern has a set of grid points separated by someperiod, p. At some distance away from the projector, the pattern spans afield of view given by a vertical and horizontal distance, H and Y. Fortraditional projectors, 30,000 grid points at a maximum will fill that

${\frac{H}{p}\left( \frac{Y}{P} \right)} = {30,000.}$

field of view such that the product In embodiments of themetasurface-polarization based solution, the optic projects one patternwith a period, p, and a second pattern, also at a period, p, but with alinear offset of p+p/2 such that a new grid point is projected at eachhalf period. The net result is that within the same field of view, H andY, the density of grid points can be doubled using themetasurface-enabled 3D systems in accordance with embodiments.

Finally, because two unique and distinguishable patterns can begenerated from systems in accordance with embodiments, such systems canalso be optimized for both short distance (<1 m) and long distance (>1m) 3D imaging. For example, certain patterns can be configured todistinguish objects that are a short distance from the device, whiledifferent patterns may be configured to distinguish patterns that are ata greater distance from the device. In such embodiments, it would bepossible to use a single device to create, e.g., pattern 1 withpolarization 1 for short distance measurement and pattern 2 withpolarization 2 for long distance measurement in a single-shot.

Embodiments for Incorporating Metasurface Elements into Imaging Systems

In some embodiments, the integration of multiple metasurface elements(two or more, for example), using methods such as those described inFIGS. 7 and 8 allow the combined system to achieve functionalitynecessary for practical CMOS camera imaging. Specifically, CMOS cameras,(such as those used in cell phones, computers, tablets etc., forcollecting images of a scene of visible light or in the infrared forbiometric authentication), require the imaging system to have anincreased field-of-view (FOV), independent control of the chief rayangle (CRA) as a function of field height at the CMOS image sensor, andminimal optical distortion of the scene being imaged. These terms willbe understood to have a meaning conventional to those skilled in theart. For traditional imaging systems, comprised of refractive lenses, asmany as five or six unique lenses must be combined to perform thisfunction. Moreover, implementing one metasurface element in such imagingsystems does not provide enough degrees of freedom to adequately controlthese parameters (CRA, FOV and minimizing distortion). However, bycombining multiple metasurfaces, each with a unique and independentphase profile, an imaging system with a wide FOV, controllabledistortion and controllable CRA can be realized in accordance withembodiments.

Referring to FIG. 13, a ray-tracing diagram through an exemplaryembodiment of a system with two metasurface elements (130 & 132)combined on a single substrate (134) in accordance with embodiments isprovided. In various such embodiments the metasurface elements on eitherside of the substrate are formed to have the same height. (Although notdescribed in detail here, it will be understood that these metasurfaceelements could be fabricated using methods as described in any of theprevious figures and combined using processes such as those described inFIG. 5, for example. In many such embodiments the metasurface elementsmay be formed from films simultaneously deposited on the two sides ofthe substrate using a suitable conformal deposition process, such as,for example, low pressure chemical vapor deposition or atomic layerdeposition.) In this exemplary embodiment, the two metasurface elementshave been configured such that in combination they are able to form agood image across a wide FOV (±44 degrees in this example, however, itwill be understood that this is not a limiting case). Embodiments ofsuch a two metasurface system, as shown, have been surprisingly found tonaturally produce focused rays at the plane of the filter and at theimage plane that are telecentric (i.e., having 0 degree CRA). In short,while traditional refractive designs require complex, many-elementsystems to realize such telecentric designs, in accordance withembodiments only two metasurface elements are needed to achieve similartelecentricity. This telecentricity in turn leads to improved opticalproperties. In particular, the low (e.g., zero or near zero degree CRA)allows for a narrowing of the bandwidth of the optical filter (136) fornarrowband applications. In traditional refractive designs, especiallyfor compact mobile applications, CRAs in are typically on the order of15 degrees to 30 degrees. These larger CRAs in turn require the filterbandwidth to be significantly increased allowing for more ambient lightto enter the detector. In narrowband applications (e.g., a near IR VCSELarray), such ambient light can be a persistent noise source. Thus,embodiments of a combined metasurface/filter system such as that shownin FIG. 13 allow for better ambient light performance.

An additional attribute of embodiments of such a telecentric design isthat the metasurface system provides a more uniform illumination at theimage sensor (referred to by those in the art as “relativeillumination”). Embodiments of the metasurface system also provide anadditional design variation with respect to traditional refractive lenssystems. Typical CMOS image sensors (CIS) require a microlens to beassociated with each pixel. Because there is a large variation in CRAacross a given sensor plane that is inherent to refractive opticalsystems, the microlens array on the CIS also requires a complex CRAspecification. However, in embodiments of metasurface systems asdescribed herein, the CRA of the microlens array may be configured to bea constant 0 degrees across the CIS allowing for greater simplicity inthe design and fabrication of the microlens array. Alternatively, incertain implementations the microlens array may be completely removedfrom the CIS, saving a process step in CIS production.

Although the embodiments of metasurface systems for use with CMOSsensors have thus far been shown with two metasurface elements onopposite sides of a single substrate, in various other embodiments thetwo metasurface elements may be disposed on separate substrates. Anexemplary embodiment of such a system is illustrated in FIG. 14. Asshown, in many such embodiments the metasurface elements are disposed ontwo separate substrates (138 & 140) with an air gap (142) disposedbetween the two elements. One advantage of such embodimentsincorporating an air gap is that the light rays can be bent farther overa shorter distance, d, in air than in a glass substrate allowing for agreater widening of the illumination zone with a shorter separationbetween metasurface elements, thus allowing for a decrease in theoverall form factor of the metasurface optical system. As shown in FIG.14, in various embodiments the metasurface elements are disposed on theair gap (142) facing surfaces of the substrates (138 & 140). Such animplementation allows for the protection of the metasurface elementsfrom environmental contamination. Additionally, such embodiments allowfor the outward face of the imager side substrate (140) to remainunpatterned, allowing for the direct integration of an optical filter(144) on the substrate. Although in the embodiments illustrated in FIG.14 the metasurface elements are arranged to face inward with respect tothe air gap between them, it will be understood that they may bedisposed on either surface of the two substrates. Production of themetasurface system illustrated in FIG. 15 can follow processes describedabove, such as, for example, those associated with FIG. 7.

Although the above discussion has described metasurface systemsconfigured to provide telecentric optical characteristics, in someinstances (e.g., where distortion correction is required) it isnecessary to introduce a non-zero CRA. Accordingly, embodiments are alsodirected to metasurface systems comprising at least three metasurfacescapable of controlling for FOV, distortion and CRA simultaneously. Aray-tracing diagram of an exemplary embodiment of a metasurface systemcomprising three metasurface elements having unique phase profiles isillustrated in FIG. 15. The introduction of the additional metasurfaceelement or elements, each allowing for the realization of a separatearbitrary phase profile, provides more degrees of freedom to control thepath of the light rays as compared to a typical system comprised of anequivalent number refractive elements. For example, to duplicate theoptical function of a system composed of three metasurfaces, inaccordance with embodiments, may require 6-7 refractive optical elementsin a conventional system. As such the comparative metasurface system mayreduce the overall thickness of such an imaging system by at least 50%while achieving equivalent or even improved performance.

Turning to the metasurface system itself, as shown in FIG. 15 such animaging system may comprise three or more metasurface elements (150, 152& 154) disposed on two or more substrates (156 & 158). As previouslydiscussed, these metasurface elements can be comprised of any suitabledielectric material, especially those that have minimal absorption atthe wavelength of interest. As shown, in various embodiments the firsttwo metasurface elements (150 & 152) may impart a telecentric opticalcharacter on the incoming light, while the third metasurface (154)(e.g.,the closest to the filter (156) and imager may impart a furtherspreading or bending to the light thus imparting non-zero CRA to thelight impacting the imager. Although a specific arrangement ofmetasurface elements and substrates is shown in the system illustratedin FIG. 15, such a diagram is meant to serve as an example and does notlimit the current disclosure to this exact system response. Regardlessof the specific arrangement of elements, fabrication of such ametasurface element can follow the processes described above, such as,for example, that shown and described in relation to FIG. 6.

Using such three metasurface element systems according to embodiments,it is possible to control CRA and thus minimize grid distortion in CMOSimage sensors. For example, FIG. 16 provides a data plot illustratingthe resulting control of the CRA as a function of field height at theCMOS image sensor for an imaging system based on the embodiment shown inFIG. 15. This is an exemplary case and the control of the CRA as afunction of field height can take on other functional forms rather thanthe linear case shown below. Similarly, FIG. 17 provides a griddistortion plot for an imaging system based on the embodiment shown inFIG. 15. As shown, embodiments of such an imaging system allows for theminimization of grid distortion to less than 5% over the entire FOV ofthe imaging system.

Embodiments for Incorporating Metasurface Elements into Imaging/SensingSystems

Given the advantages described of using metasurface elements accordingto embodiments on both sensing optics and on projection optics, variousembodiments are directed to metasurface systems configured for use in acombined illumination-sensing module. Referring to FIG. 18, a schematicof an integrated illuminator and sensor system according to embodimentsis provided. As shown, in such embodiments an illuminator (160) having aplurality of spacers (162 & 162′) and metasurface elements (164 and164′), either alone or in combination with refractive elementsconfigured therewith to provide a specific radiation pattern is used toilluminate some object or scene (166). A sensor (168) (e.g., a CMOSimage sensor) with a corresponding metasurface system is used to detectthe radiation or from an image of the scene. In such embodiments, theoverall system—metasurface elements (162 & 162′), sensor (168),illuminator (160)—may be configured to operate over some particularbandwidth or at a specific wavelength of interest and may be combinedonto a single platform (170). The illuminator and sensor metasurfaceelements (162 & 162′) may be configured to work an any polarization ofthe electric field. Embodiments of such combined systems may be used ona computer, a cell phone, a television monitor, a wall-mounted unit, acredit card, tablet, mirror etc.

As discussed above in relation to FIGS. 12A to 12C, metasurfaces alsoallow unique functionality to be imprinted on two orthogonalpolarizations. Thus, various embodiments of metasurfaceilluminator-sensing systems can also be co-designed taking polarizationas an additional optimization variable. Referring to FIG. 19, aschematic of an integrated illuminator system that also acts on thepolarization of the radiation field is provided. As shown, in one suchexemplary embodiment, an illuminator (172) with one or more metasurfaceelements (174 & 174′) along with suitable spacers (176 & 176′) anoptional refractive elements is used to illuminate a scene or object(178). The metasurface elements in such embodiments have been designedsuch that for any two orthogonal polarizations of light, two unique andindependent radiation patterns can be produced. A sensor (180) with acorresponding set of metasurface elements is used to collect the lightreflected from the scene. As shown, the illuminator and sensormetasurface elements have been configured to work cooperatively suchthat the two orthogonal polarizations used to produce the radiationpattern form two unique images on the sensor. The system—metasurfaces(174 & 174′), sensor (180), illuminator (172)—according to embodimentsmay be optimized for operation over some bandwidth or at a specificwavelength of interest and may be combined onto a single platform (182).It will be understood that the illuminator and sensor metasurfaceelements in accordance with embodiments may be configured to work an anypolarization of the electric field. The combined system according toembodiments may be used on a computer, a cell phone, a televisionmonitor, a wall-mounted unit, a credit card, tablet, mirror etc.

Embodiments of Metasurface Element Material Systems

As previously discussed, each individual metasurface element in anyoptical system, whether there be one or many metasurface elementscomprising the system, has some specific 2D phase and transmissionfunction, ϕ(x, y) and t(x, y), that it carries out. While in generaleach metasurface element may have a unique distribution of phase andtransmission, the nanostructure features that comprise any metasurfaceelement embedded in the same material, with the same base composition,and at a specific wavelength are identical. In most practical singlewavelength applications, the transmission is desired to be maximized(near 1) and uniform across the metasurface while the phase need onlytake on values between 0 and 2π. In summary, for some wavelength ofinterest, material system (metasurface material and embedding material),fixed thickness and element spacing, one need only find a set ofin-plane dimensions of the comprising nanostructure features such thatphase delays from 0 to 2π can be imprinted on an incident light field.Thus for various embodiments of metasurface element designs at the fixedmaterial and wavelength conditions, the only variable from design todesign is the distribution of those nanostructure features across themetasurface element. Accordingly, various embodiments of metasurfaceelement material conditions suitable for performing specific opticalfunctions over desired wavelength ranges are described. Although thefollowing discussion sets forth embodiments of metasurface elements andsystems, and processes for fabricating such metasurface elements andsystems. It will be understood that the following embodiments areprovided only for exemplary purposes and are not meant to be limiting.

Referring to FIG. 20, phase and transmission maps for embodiments ofmetasurface elements comprising silicon pillars embedded in SiO₂ areprovided. The top left diagram provides a heat map of transmission as afunction of pillar diameter and height, color scale shown to the right.The top right diagram provides a phase map as a function of pillardiameter and height. The bottom left provides a diagram of a line scanof transmission as a function of pillar diameter at a fixed height of600 nm. The bottom right provides a diagram of a line scan of relativephase as a function of pillar diameter for a fixed height of 600 nm. Itwill be understood that using these diagrams it is possible to determinea specific set pillar diameters and heights for a specific transmissionand phase across all suitable wavelengths in accordance withembodiments, and also specific diameters for a height of 600 nm. In manyembodiments, the pillar height may vary from 500 to 1000 nm and thepillar diameter from 100 to 300 nm. In various other embodiments, thepillar diameter may vary from 100 to 200 nm, and the pillar height from500 to 800 nm. In various other embodiments at a pillar height of 600nm, the pillar diameter may vary from between 100 to 300 nm. Thespecific heights and diameters represent a local optimum for thetransmission of the elements but other pillar heights may be used inembodiments as required by the design of the specific optical system.

Referring to FIG. 21, phase and transmission maps for embodiments ofmetasurface elements comprising silicon pillars in air are provided. Thetop left diagram provides a heat map of transmission as a function ofpillar diameter and height, color scale shown to the right. The topright diagram provides a phase map as a function of pillar diameter andheight. The bottom left provides a line scan of transmission as afunction of pillar diameter at a fixed height of 480 nm. The bottomright provides a line scan of relative phase as a function of pillardiameter for a fixed height of 480 nm. It will be understood that usingthese diagrams it is possible to determine a specific set pillardiameters and heights for a specific transmission and phase across allsuitable wavelengths in accordance with embodiments, and also specificdiameters for a height of 480 nm. In many embodiments, the pillar heightmay vary from ˜1 to 500 nm and the pillar diameter from 100 to 350 nm.In various other embodiments, the pillar diameter may vary from 100 to250 nm, and the pillar height from 150 to 500 nm. In various otherembodiments at a pillar height of 480 nm, the pillar diameter may varyfrom between 100 to 280 nm. The specific heights and diameters representa local optimum for the transmission of the elements but other pillarheights may be used in embodiments as required by the design of thespecific optical system.

Referring to FIG. 22, phase and transmission maps for embodiments ofmetasurface element comprising TiO₂ pillars in air are provided. The topleft diagram provides a heat map of transmission as a function of pillardiameter and height, color scale shown to the right. The top rightdiagram provides a phase map as a function of pillar diameter andheight. The bottom left diagram provides a line scan of transmission asa function of pillar diameter at a fixed height of 975 nm. The bottomright provides a line scan of relative phase as a function of pillardiameter for a fixed height of 975 nm. It will be understood that usingthese diagrams it is possible to determine a specific set pillardiameters and heights for a specific transmission and phase across allsuitable wavelengths in accordance with embodiments, and also specificdiameters for a height of 975 nm. In many embodiments, the pillar heightmay vary from 300 to 1000 nm and the pillar diameter from 100 to 350 nm.In various other embodiments, the pillar diameter may vary from 100 to300 nm, and the pillar height from 300 to 400 nm and/or 700 to 1000 nm.In various other embodiments at a pillar height of 975 nm, the pillardiameter may vary from between 100 to 300 nm. The specific heights anddiameters represent a local optimum for the transmission of the elementsbut other pillar heights may be used in embodiments as required by thedesign of the specific optical system.

Referring to FIG. 23, phase and transmission maps for embodiments ofmetasurface elements comprising amorphous silicon pillars embedded in abenzocyclobutane (BCB) polymer are provided. The top diagram provides aline scan of transmission as a function of pillar diameter at a fixedheight of 590 nm and element period of 400 nm. The bottom diagramprovides a line scan of phase as a function of pillar diameter at afixed height of 590 nm and element period of 400 nm. It will beunderstood that using these diagrams it is possible to determine aspecific set pillar diameters and heights for a specific transmissionand phase across all suitable wavelengths in accordance withembodiments, and also specific diameters for a height of 590 nm. In manyembodiments, at a pillar height of 975 nm, the pillar diameter may varyfrom between 100 to 300 nm. In various other embodiments, the pillardiameter made vary from 100 to 225 nm. The specific heights represent alocal optimum for the transmission of the elements but other pillarheights may be used as required by the design of the specific opticalsystem.

Referring to FIG. 24, phase and transmission maps for embodiments ofmetamaterial elements comprising amorphous silicon pillars embedded in asilicon dioxide are provided. The top diagram provides a line scan oftransmission as a function of pillar diameter at a fixed height of 600nm and element period of 350 nm. The bottom diagram provides a line scanof phase as a function of pillar diameter at a fixed height of 600 nmand element period of 350 nm. It will be understood that using thesediagrams it is possible to determine a specific set pillar diameters andheights for a specific transmission and phase across all suitablewavelengths in accordance with embodiments, and also specific diametersfor a height of 600 nm. In many embodiments, at a pillar height of 600nm, the pillar diameter may vary from between 100 to 275 nm. In variousother embodiments, the pillar diameter made vary from 100 to 175 nm. Thespecific heights represent a local optimum for the transmission of theelements but other pillar heights may be used as required by the designof the specific optical system.

In other embodiments tests were also conducted on amorphous-Simetasurface features embedded in SU8, and it was found such surfaceshaving a pillar height of 675 nm and a pillar diameter from 100 to 300nm are suitable for use. In addition, amorphous-Si metasurface featuresin air having a pillar height of 600 nm and a pillar diameter from 100to 300 nm with an element spacing of 450 nm may be suitable inaccordance with various embodiments.

Although specific combinations of metamaterials and embedding materialsare described above, it will be understood that similar maps ofmetasurface feature, transmissivity and phase may be made in accordancewith embodiments of the invention.

DOCTRINE OF EQUIVALENTS

Accordingly, although the present invention has been described incertain specific aspects, many additional modifications and variationswould be apparent to those skilled in the art. It is therefore to beunderstood that the present invention may be practiced otherwise thanspecifically described. Thus, embodiments of the present inventionshould be considered in all respects as illustrative and notrestrictive.

What is claimed is:
 1. An illumination device comprising: a verticalcavity surface emitting laser (VCSEL) array; and a plurality ofmetasurface elements arranged in a planar array such that light emittedfrom the VCSEL array passes through the planar array of metasurfaceelements, and wherein the planar array of metasurface elementscollimates light from the VCSEL array and multiplies the VCSEL in thefar field.
 2. The illumination device of claim 1, wherein the focallength of the planar array of metasurface elements is equal to thedistance from the top of the VCSEL array to planar array of metasurfaceelements.
 3. The illumination device of claim 1, wherein the metasurfaceelements comprise amorphous silicon and the VCSEL array is operating ata wavelength of 940 nm.
 4. The illumination device of claim 1, whereinthe first polarization is parallel to the second polarization.
 5. Theillumination device of claim 1, wherein the collimated light from thelens is telecentric across the planar array of metasurface elements. 6.An illumination device comprising: a vertical cavity surface emittinglaser (VCSEL) array; and a plurality of metasurface elements arranged ina planar array such that light emitted from the VCSEL array passesthrough the planar array of metasurface elements, wherein the lightpassing through the planar array of metasurface elements comprises afirst polarization light including a first dot pattern and a secondpolarization light including a second dot pattern, and wherein first dotpattern is denser in the far field than the second dot pattern, andwherein the planar array of metasurface elements collimates light fromthe VCSEL array with equal focal length for the first polarization andthe second polarization.
 7. The illumination device of claim 6, whereinthe focal length of the planar array of metasurface elements is equal tothe distance from the top of the VCSEL array to planar array ofmetasurface elements.
 8. The illumination device of claim 6, wherein themetasurface elements comprise amorphous silicon and the VCSEL array isoperating at a wavelength of 940 nm.
 9. The illumination device of claim6, wherein the first polarization is parallel to the secondpolarization.
 10. The illumination device of claim 6, wherein thecollimated light from the planar array of metasurface elements istelecentric across the planar array of metasurface elements.
 11. Theillumination device of claim 6, wherein the first dot pattern israndomly distributed and the second dot pattern is spaced on an equalgrid.
 12. An illumination device comprising: a vertical cavity surfaceemitting laser (VCSEL) array; and a plurality of metasurface elementsarranged in a planar array such that light emitted from the VCSEL arraypasses through the planar array of metasurface elements, wherein thelight passing through the planar array of metasurface elements comprisesa first polarization light including a first dot pattern and a secondpolarization light including a second dot pattern, and wherein the firstdot pattern has a narrower field of illumination than the second dotpattern.
 13. The illumination device of claim 12, wherein, in the firstdot pattern and the second dot pattern, the field of illumination iscontrolled by the number of dots in the first dot pattern and the seconddot pattern but the collimation functionality is substantiallyidentical.
 14. The illumination device of claim 12, wherein the firstdot pattern is randomly distributed and the second dot pattern is spacedon an equal grid.
 15. The illumination device of claim 12, wherein thefocal length of the planar array of metasurface elements is equal to thedistance from the top of the VCSEL array to planar array of metasurfaceelements.
 16. The illumination device of claim 12, wherein themetasurface elements comprise amorphous silicon and the VCSEL array isoperating at a wavelength of 940 nm.
 17. The illumination device ofclaim 12, wherein the first polarization is parallel to the secondpolarization.
 18. The illumination device of claim 12, wherein thecollimated light from the planar array of metasurface elements istelecentric across the planar array of metasurface elements.
 19. Theillumination device of claim 12, wherein the second dot pattern has anequivalent dot pattern at an offset to the first dot pattern so that theneighboring dots of the first dot pattern and the second dot pattern inthe illuminated field have orthogonal polarizations.
 20. An illuminationdevice comprising: a vertical cavity surface emitting laser (VCSEL)array; and a plurality of metasurface elements arranged in a planararray such that light emitted from the VCSEL array passes through theplanar array of metasurface elements, wherein the light passing throughthe planar array of metasurface elements comprises a first polarizationlight including a dot pattern in the far field and a second polarizationlight including an arbitrary radiation pattern with an angle-dependentintensity in the far field, and wherein the planar array of metasurfaceelements collimates light with equal focal length for both the firstpolarization light and the second polarization light.
 21. Theillumination device of claim 20, wherein the focal length of the planararray of metasurface elements is equal to the distance from the top ofthe VCSEL array to planar array of metasurface elements.
 22. Theillumination device of claim 20, wherein the metasurface elementscomprise amorphous silicon and the VCSEL array is operating at awavelength of 940 nm.
 23. The illumination device of claim 20, whereinthe first polarization is parallel to the second polarization.
 24. Theillumination device of claim 20, wherein the collimated light from theplanar array of metasurface elements is telecentric across the planararray of metasurface elements.
 25. The illumination device of claim 20,wherein the arbitrary radiation pattern has a batwing pattern, top hatpattern, or super-gaussian pattern.